JPH0194207A - Measurement of thickness for concrete plate or the like - Google Patents

Abstract

PURPOSE:To facilitate the measurement of the thickness of a concrete slab or the like, by receiving an ultrasonic wave propagated through an object to be inspected varying a distance between probes to find a transition point where a change in propagation time becomes discontinuous. CONSTITUTION:A probe 2 for transmission and a probe 3 for reception are arranged as opposed to each other on the surface 1a of an object 1 to be inspected to measure a propagation time (t) lengthening a distance L between the probes gradually. Here, at first, the time (t) increases continuously almost at a fixed ratio with an increase in the distance L. But when the distance L almost doubles the thickness of an object 1 to be measured, a transition point appears where the increase of the time (t) becomes discontinuous. After the appearance of the transition point, the time (t) increases continuously with an increase in the distance L. Here, it is presumed that the transition point appears because of a difference in the propagation path before and after effect is given from a bottom surface and a delay in the sound velocity with a mode change. Thus, the thickness of a concrete plate can be measured with a distance between the probes as evaluation index at the transition point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring the thickness of a concrete plate or the like using ultrasonic waves.

Concrete plates, etc. here are plate-shaped non-metallic materials, such as concrete, asphalt, which are mixed and solidified materials of different particle sizes and materials, tiles, porcelain such as insulators, and bricks. Refers to sintered and solidified fine powder, limestone, marble, and other rocks. Further, the thickness dimension to be measured is about 20 mm or more.

[Prior Art] Conventionally, many methods have been used to measure the thickness of a solid, such as a method that utilizes ultrasonic resonance within a plate, and a method that is determined from the reciprocating time of an ultrasonic pulse within a plate. However, these measurement methods mainly measure metal materials such as steel, and when these methods are applied to non-metallic materials with a high degree of attenuation such as concrete, the frequency used must be between 20 k IIz and 300 k IIz. Since it has to be at a low frequency of k &, the ultrasonic wave generated by the transmitting transducer has a pulse of a number M that targets materials with low attenuation such as steel.
This is much longer than in the case of a frequency of Hz, and the reflected wave is buried in the transmitted pulse, making it impossible to distinguish between the transmitted pulse and the received wave, making it impossible to measure the thickness. Furthermore, the conventional method described above is a one-probe method using a vertical probe, but this can be changed to, for example, a two-probe method in which transmitting and receiving probes are arranged side by side on the same plane of concrete 1 to plate. It is also possible to measure it, but even in this case, the frequency of the probe used is low as mentioned above, so it is non-directional, and generally most of the ultrasonic waves incident from the transmitting probe into the concrete plate are It is said that the waves propagate along a parabolic path within the concrete plate to the receiving probe without reaching the bottom surface, and as a result, the reflected waves from the bottom surface are not substantially obtained, making it impossible to measure the thickness. In this case, it is conceivable to increase the size of the vibrator in order to increase the directivity gain, but there is a natural limit to the dimensions for electrically vibrating the vibrator, and the above phenomenon cannot be avoided. As described above, in the past, there was no method of measuring the thickness of a concrete plate or the like using ultrasonic waves, and the actual situation was that the method relied on measuring tools such as scales.

[Problems to be Solved by the Invention] In view of the above problems, the present invention provides a measuring method that can easily and accurately measure the thickness of concrete 1, boards, etc. using ultrasonic waves. The purpose is to provide.

[Means for Solving the Problems] In order to achieve the above object, the method for measuring the thickness of a concrete plate, etc. of the present invention is such that transmitting and receiving probes are brought into contact with the same plane of the object. A low-frequency ultrasonic wave is injected into the subject from a reliable probe, and the ultrasonic wave propagated through the subject is received by a receiving probe while changing the distance between the probes, and the received signal is The thickness of the concrete plate, etc. is measured using the distance between the probes at the position of the transition point where the propagation time does not change continuously but becomes discontinuous at a constant ratio to the amount of change in the distance between the probes as an evaluation index. It is characterized by

[Function] The relationship between the propagation time of the received signal and the distance between the probes shown in the configuration shown in section 2 is that if the distance between the probes is shorter than the plate thickness, the ultrasonic waves will travel in a parabolic shape inside the object such as concrete. Ryokan M' with a route like? On the other hand, if the distance between the probes is longer than the plate thickness, the ultrasonic waves incident into the subject will follow the parabolic path described above until they reach the bottom. = 3- After that, there is a relationship in which the signal is influenced by the bottom surface and is propagated and received on a path different from the parabolic path. While the ultrasound propagates along the parabolic path, the propagation time increases continuously at a nearly constant rate as the distance between the probes increases. When the propagation time increases to approximately twice that of , a transition point appears where the increase in propagation time becomes discontinuous due to the difference in the propagation path due to the effect of the bottom surface. After the appearance of this transition point, the propagation time continuously increases as the distance between the probes increases, depending on the propagation path influenced by the bottom surface.

The above transition point appears as a difference in propagation time between the propagation distance due to the difference in the propagation path before and after the influence of the bottom surface of the object and the sound speed slowed by mode conversion. The thickness of a concrete plate, etc. is measured using the distance between the probes at the position of this transition point as an evaluation index.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a method for measuring the thickness dimension (hereinafter referred to as block thickness) d of a concrete block. In the figure, 1 is a concrete block to be inspected, length (thickness is d) x
It is a □ rectangular parallelepiped with no reinforcing bars and the width x length dimensions are 200 x 200 x 800 (unit: lff11). In addition, the nominal strength of the concrete block is 210 kg/c.
d, the concrete mix is as shown in the table below. The average sound speed of the transverse wave (S) in the object 1 is 3230.5 m.
/sec. Table 1 2 is the transmitting probe, 3 is the receiving probe, and test subject 1
are disposed facing each other on the surface Ja of the surface Ja, and are connected to a low frequency flaw detector (not shown). Probes 2 and 3 used
is a transverse wave vertical probe (model 0.IZ4ON-8H), frequency 100 kHz, transducer material is lead zirconium titanate ceramic (PZT), transducer diameter D = 40mv+
It is.

To measure the propagation time, first bring the probes 2 and 3 close together and start with a short distance between the probes, gradually increase the distance between the probes, and set the measurement pitch to 5ORI + pitch, L = 1001 m.
I ~ 700mm. The measurement results are shown in Figure 2. The horizontal axis in the figure is the distance between the probes (distance between the centers of the probes)
L (mm), and the vertical axis indicates propagation time t (μS). O in the diagram
The mark is the measured value, and as the distance between the probes increases, the propagation time t
It can be seen that the number is also increasing.

However, this relationship is not continuous at a constant rate, and a transition point appears where the inter-probe distance becomes discontinuous, especially between 400 and 450 nwn.

The reason for the appearance of this transition point is that in this example, the relationship between the inter-probe distance and the propagation time t changes linearly at an almost constant rate until the inter-probe distance reaches 400 mm. There is a relationship between L = 400 and 450 m, which is the plate thickness d of the object 1.
This is approximately twice as much as the ultrasonic wave incident on the subject 1, and furthermore, the relationship between the two changes continuously in a non-linear relationship different from that up to L = 400 mm when L is 450 mm or more. Influenced by the bottom surface 1b, L = 40
From 01[111 to L = 450+ff++, a difference in propagation time occurs due to an increase in propagation distance due to a difference in propagation path and a decrease in sound speed due to mode conversion, and this difference causes a transition point to appear. It is estimated to be. In order to clarify this estimation, the inventor of the present application proposed that when the distance between the probes is shorter than the plate thickness d as shown in FIG. When the probe 3 is in the position shown in (b), the parabolic path, which is considered to be the propagation path of conventional ultrasonic waves, is set so that the center of both probes 2.3 is the center of a circle (for example, (a) ), use A) in the figure, and use a circular arc (semicircle) whose radius is the distance to the end face of the probe.
Assume that a transverse wave (S) propagates as a path, and as the distance between the probes becomes longer, the wave propagates in an arc shape whose center is C in the figure where the arc is at the bottom point and whose radius is the distance to the end face of the probe. The transverse wave (S) hit the bottom surface 1b and is mode-converted into a surface propagation wave (R), which propagates along the bottom surface 1b as shown by the dotted line in the figure, and then becomes a transverse wave ( Assuming that the mode is converted to S) and received by the probe 3, the propagation time t as the distance between the probes increases was calculated using the following equation. That is, here, Q is the distance that the surface propagating wave (R) propagates on the bottom surface 1b as shown in Figure 1, and 0 is the mode conversion of the surface propagating wave (R) to a transverse wave (S) as shown in the figure. VS is the sound speed of the transverse wave (S), and vR is the sound speed of the surface propagation wave (R).

The values calculated using the above equation (1) are shown in solid lines in FIG. 2, and the values calculated using equation (2) are shown in FIG. 2 as dotted lines. Both the solid line and the dotted line are in good agreement with the measured values, and by dividing the propagation distance by the determined propagation time t, a sound velocity value of approximately 3230 m/see is obtained, which is the same as that of the transverse wave (S) of the object 1 determined earlier. equal to the average speed of sound. From these results, find the propagation path and propagation time t of the ultrasonic wave as the distance between the probes changes.'' Equations (1) and (2) are correct, and at the same time, the estimation of the cause of the appearance of the transition point is also valid. It turns out that it is something.

Therefore, by calculating the position where the propagation time t becomes discontinuous using equations (1) and (2) above, or detecting a transition point by displaying the calculated value on a CRT, etc., the probe at that position can be detected. ]/2 of the distance between the end faces is determined as the plate thickness of concrete 1~. Specifically, in the above example,
Since the transition point is between the distance between the probes of 400cm and 450m, 1/2 of the distance between the end faces of the probes is ]-80nw
n-205 mm, which indicates that the measurement is accurate with respect to the actual plate thickness d = 200 nm.

Next, an example in which the present invention is applied to an actual concrete product will be described. The product to be tested is a road curb.
Dimensions are thickness dx width x length 150 x 120 x 600 (
It is approximately a rectangular parallelepiped with unit n11). The average sound speed VS of transverse waves of this subject is 2853 m/see, and the average sound speed VR of surface propagation waves is 1041 m/see. Further, the probe used for the measurement and the measurement conditions were the same as those shown in FIG. 1 above.

Figure 3 shows the measurement results. The 0 mark in the figure is the measured value, and the horizontal axis
The vertical axis and the nine-dot straight line in the figure indicate the same as in FIG. 2 above. As can be seen from the figure, the pattern of change in propagation time t as the distance between the probes changes is the same as in the case of Fig. 2, and the position of the transition point where the change in propagation time t becomes discontinuous is It is clearly shown that the distance between the tentacles is between 300nwn and 350m. This shows that since 1/2 of the distance between the end faces of the probe is 130 mm to 155 m, the measurement was performed with good accuracy for the actual curb thickness cl" 150 mm. This measurement accuracy is By measuring at a fine pitch before and after the transition point, the position of the transition point can be specified in a narrower range, and further improvement can be achieved.

In addition, although the above embodiment was explained with reference to concrete,
Before other than concrete! Of course, it is also possible to measure porous plate-shaped non-metallic materials such as porcelain and rocks in the same manner as in the above embodiment.

[Effects of the Invention] As explained above, the present invention provides a transition point at which the propagation time of the ultrasonic waves received while propagating through the object does not change continuously with the amount of change in the distance between the probes, but becomes discontinuous. Since the thickness of a concrete plate, etc. is measured using the distance between the probes at the position as an evaluation index, there is a practical effect that the thickness can be easily and precisely measured.

[Brief explanation of the drawing]

The drawings are all detailed explanatory diagrams of the present invention, with Fig. 1 showing the method for measuring the thickness of a concrete block, Fig. 2 showing the measurement results measured in accordance with Fig. 1, and Fig. 3 showing the actual thickness of the concrete block. FIG. 2 is a diagram showing an example of measurement results for a concrete product.

Claims (1)

[Claims] 1. Contact the transmitting and receiving probes on the same plane of the subject, inject low-frequency ultrasonic waves into the subject from the transmitting probe, and collect the ultrasonic waves that propagated through the subject. The receiving probe receives the signal while changing the distance between the probes, and the propagation time of the received signal does not change continuously but becomes discontinuous at a constant ratio to the amount of change in the distance between the probes. A method of measuring the thickness of concrete plates, etc. using the distance between the probes at the transition point as an evaluation index.